Safety shield for explosively driven tools



R. T. cATLlN ET AL 2,700,764

SAFETY SHIELD FOR ExPLosIvELY DRIVEN TooLs `2 sheets-Sheet 1 INVENTORS @05E/f7 ZCAL//v /D/i 0,4 H/c/fMA/V AT'ToR/VE Feb. l, 1955 Filed July 24, 1952 Feb. 1, 1955 R. T. CATLIN ET AL SAFETY SHIELD FOR ExPLosIvELY DRIVEN TooLs 2 Sheets-Sheet 2 Filed July 24, l952- Vl Mmm .E 07A N MAM R E? .m wrm Hr 17H A @A RP v.. B

United States Patent-O SAFETY SHIELD FOR EXPLOSIVELY DRIVEN TOOLS Robert T. Catlin, Stratford, and Paul Hickman, Trumbull, Conn., assignors to Remington Arms Company, Inc., Bridgeport, Conn., a corporation of Delaware Application July 24, 1952, Serial No. 300,716

3 Claims. (Cl. 144.5)

This invention relates to a shield or guard for use on an explosively driven tool which is designed to minim1z e or prevent altogether the projection of loose flying partlcles as an incident to the normal operation of the tool. Accompanying the penetration of the work there is usually some spalling of a concrete surface, and fragments of rust, scale, or paint are frequently chipped from metallic surfaces. To these loose materials there Amust be added fragments of any gas sealing devices used in the bore of the tool and an occasional stud which breaks, chips, or ricochets on impact with the work surface. All of these materials are present in more or less quantity in the region adjacent the point in whi-ch the stud penetrates the work surface and, in the absence of exceptionally effective safety guards, are swept laterally at high velocities by the muzzle blast of high pressure gas from the barrel of the tool. The lateral projection of such materials places severe limi-tations upon the use of explosively operated tools and, in some jurisdictions, the use of such tools with the types of shields heretofore devised is forbidden by law or by industrial safety regulations.

The major object of our invention is to provide a shield which ret-ains any l-oose particles within the confines of the shield.

There have been heretofore devised shields which prevent the rearward projection of such loose particles which are fairly effective in protecting the actual operator of the tool. Such a shield is shown in the pending applic-ation of Walker, Serial Number 225,146, filed May 8, 1951, and issued as Patent No. 2,645,772, on July 21, 1953, and an improvement thereon is shown in the pending application of Catlin, Serial Number 252,949, filed October 24, 1951 and i-ssued as Patent No. 2,699,716, on February 23, 1954. The tool of the first mentioned of these applications is provided with a safety device which will not be operated to permit firing unless the shield is firmly pressed against the work, which may be defined as the surface of the wall, fioor, bea-m, or other structural member which is to be penetrated by a driven stud. In the Catlin application above identified, there is shown an improvement upon the shield of the Walker application designed to require not only that the shield be pressed firmly against the surface of the work but that the barrel of the tool should also be substantially perpendicular to the work surface before the safety device will permit the operation of the tool.

The present invention contemplates a further improvement which may retain all the advantages of the two prior applications referred to, in requiring that the shield `be pressed firmly against the work surface and be substantially normal thereto. To these advantages our present shield design adds that of confining within the shield substantially -all flying particles, thus avoiding the lateral projection which has been unavoidable with the prior types of shields.

In general, these objectives have been accomplished by the provision of a boxlike shield which is spring-urged against the work surface and which, with the work surface, forms a chamber enclosing the muzzle of the barrel. The new shield is so mounted upon the tool that the tool may recoil relative to the work surface without disengaging the edge of the shield box therefrom. Preferably, the shield will contain initially or be capable of providing during operation an expansion chamber within which some of the blast of escaping gases may be dissipated, Although the shield may be vented to permit expanding gas to esc-ape, such vents should be of such diice mensions that no particles of matter of substantial size may escape.

The exact nature of the invention as well as other objects and advantages thereof will become apparent from consideration of the following specification referring to the attached drawings in which:

Fig. 1 is a side elevational view, partially in longitudinal section along the line lkl of Fig. 4, showing a complete tool embodying the present invention.

Fig. 2 is a fragmentary longitudinal sectional View, showing the fact that the scar remains locked when the tool is pressed against the work surface at a position inclined thereto.

Fig. 3 is a View similar to Fig. 2, showing the unlocking of the sear when the tool is pressed against the work surface in a position substantially perpendicular thereto.

Fig. 4 is a plan view, partially in section, on the line 4 4 of Fig. 1.

Fig. 5 is a view generally similar to Fig. 3, showing a modified form of our invention as applied to a known and competitive type of tool.

The illustrative tool shown in the drawings comprises a barrel 1 provided with a chamber 2 adapted to receive a cartridge which is provided with a projectile in the form of a stud or other element to be driven into or against the work. The chamber is closed by a breech block 3 which is apertured to provide for the movement of a firing pin 4 to engage the cartridge primer. Bree-ch block 3 is secured in a frame or housing 5 which houses the firing mechanism and is extended into a handle or grip 6. The firing pin 4 is provided with a scar-engaging enlargement 7 and is urged forwardly by a firing spring 8. Cooperating with the soar-engaging part 7 is a sear 9 pivoted in the frame at 10 and provided with a head 11 adapted f-or displacement to release the firing pin by cam engagement with a trigger 12 which is mounted for rectilinear movement in the frame and is provided with a finger piece 13 within the grip 6. Normally, the sear is locked against firing pin releasing movement by a sear lock 14 which underlies the firing pin engaging portion 9 of the Sear and is mounted for rectilinear movement Iin the frame, being thrust forward to its effective or searlocking position by a spring 15 (Fig. l).

The barrel 1 is held in a housing or action tube cover 16 provided with an end pla-te or frame 17 to which the barrel is secured, said end plate being rotatably secured to the breech block 3 by means of the pivot bolt 1S passing through both breech block and end plate. Slidably mounted on the barrel within the action tube cover 16 is an action tube 19 t-o which is secured an action bar 20 that extends rearwardly in alignment with and is adapted to displace the sear l-ock 14, t-o permit firing. Secured to the forward end of the action tube 19 and exltending forwardly therefrom through action tube cover 16 is an action tube extension 21. A spring 22 interposed between the rear end of the action tube extension and a shoulder on the barrel normally holds the action tube assembly 19-20-21 in the forward position illustrated in Fig. l.

The tool as thus far described is substantially identical with the one shown in the aforementioned application of Walker, and is designed particularly for driving studs into difficultly penetrable materials, such as cinder block, cement block, Portland Cement concrete, and steel. The impact of the stud against aggregate materials of the concrete type tends to dislodge and forcefully expel small fragments or chips at the surface. To prevent damage and injury by such flying particles, it is desirable to provide a shield which must be firmly pressed against the surface of the wall, door, beam, or other structural member or fixture which is to be penetrated by the driven stud. For convenience in this specification and the claims appended thereto, any member to which the tool is applied for the purpose of securing a stud therein will, in accordance with well-established practice, be referred to as the wor Since the work is usually a hard and diflicultly penetrable material, it becomes important to insure that the tool be so applied to the work surface that the stud is driven in a direction substantially perpendicular to said surface rather than oblique thereto. The invention of the prior Catlin application above referred to provides not only that the tool must be held against the work, but that it must be held substantially perpendicular to the work surface to enable rotation of the sear 9 to firing position.

To this end, two assemblies were provided in the prior Catlin construction, one an action tube assembly or "action member comprising action bar 20, action tube 19, and action tube extension 21; and the other, a shield assembly slidably mounted on the reduced portion 211 of the action tube extension 21.

Our present invention is an improvement in the shield assembly and is mounted in an equivalent fashion on the action tube extension 21. The preferred embodiment of our new shield assembly comprises a sleeve 23 secured by brazing or other equivalent means to a top retaining plate 101, preferably in a position normal to the surface of that plate but eccentric with respect to the center thereof. Through the agency of rivets 102 and spacers 103, the top retaining plate is permanently attached to a bottom retaining plate 104 with suflicient space between them to permit the reception of the top plate 24 of the shield A clamping bolt 105 is permanently secured to the bottom retaining plate 104 and passes through a spacer 106 and the top retaining plate 101, where a wing nut 107 permits the two retaining plates to be drawn together tightly enough to clamp upon the top plate 24 of the shield 25. It will be noted that a circular hole 108 is provided in the top plate 24, having a diameter such that engagement with the evenly distributed spacers 103 and 106 supports the retaining plate assembly for rotation within the hole 108 when the wing nut 107 is free. Since the hole 108 is eccentric to the top of the shield 25, a wide range of adjustment is permitted with regard to the distance of the sleeve 23 from the side of the shield 25.

The present shield 25 comprises a boxlike member, conveniently but not necessarily of rectangular shape, within which the escaping gas may expand and particles of spall, etc., be trapped. We have found that if this chamber has a volume of four cubic inches, e. g., 4" square and 1/4" deep, it is quite effective in retaining the larger and more dangerous fragments of spall, etc. With substantially less than this enclosed volume, we have been unable to discern any practical advantage not shared by the flat pad type guards of the prior art. Increasing the chamber volume renders the guard much more effective, one having a volume of 24 cubic inches (e. g., 4 inches square and l1/2 inches deep) appeared to remain in substantial contact with the work throughout the firing cycle, retained both large and small particles of spall, and showed a clear and definite 4 inch square pattern of accumulated dust when the tool was removed from the work surface. No detectable particles were projected beyond the confines of the guard having a 24 cubic inch volume. The shield is necessarily made of fairly heavy steel or other material which will be resistant to the impact of a possible ricocheting stud. Narrow vent slots may be cut in the peripheral side walls with some lessening of the tendency of low volume shields to separate from the work surface, but such vents should be so small that no dangerous particles can be projected. With chambers of adequate volume, e. g., 16 or more cubic inches, vents are quite unnecessary.

Any convenient lost motion connection between the action tube assembly and the shield assembly may be provided. In the connection illustrated, the sleeve 23 of the shield assembly terminates in a shoulder 231 which has a larger diameter than the shoulder 212 on the action tube extension 21 and is thus adapted for engagement with the end face 161 of the action tube cover 16 (Figs. 2 and 3). An enlargement 232 in the bore of the sleeve 23 receives the end of a pin 233 forced into and permanently retained in a hole in the action tube extension 21 to limit the extent of sliding movement of the sleeve 23 on the action tube extension 21 to that in which the open edge 251 of the shield 25 projects fivesixteenths of an inch or more in advance of the end of the action tube extension 21. A coil spring 234 provided in engagement between the top retaining plate 101 and the end face 161 of the action tube cover 16 serves to urge the shield to so project in advance of the action tube extension. The sleeve 23 has therefore a range of movement upon the action tube extension between a position in which the edge of the shield projects in advance of the action tube extension, as shown in Fig. 1, and a position of engagement of the sleeve shoulder 231 with the shoulder 212 on the action tube extension, as shown in Fig. 2. The most convenient arrangement of the interengaging surfaces of the sleeve 23 and action tube extension 21 is to form them as right circular cylindrical surfaces, although it should be obvious that for functional purposes cylindrical surfaces of other than right circular form would be satisfactory. Accordingly, we will describe suitable surfaces as cylindrical surfaces defined by a line generatrix parallel to the axis of the barrel.

Fig. l shows the shield assembly comprising the sleeve 23, retaining plates, and shield 25 in their normal extended position on the action tube extension 21. The action tube assembly is in its foremost position with respect to action tube cover 16 and the action bar 20 is spaced some distance away from the sear lock 14. Fig. 2 shows diagrammatically the position of these parts when the tool is pressed against a solid surface in a position inclined to such surface. A small portion only of the periphery of the edge 251 of the face of shield 25 engages the work surface W. This engagement thrusts the shield assembly to the rear against the urging of the spring 234 until shoulder 231 (Fig. l) of the shield assembly engages the forward end 161 of the action tube cover. As seen in Fig. 2, the action tube assembly has been partially displaced, but still projects forwardly from the shield face into engagement with the work face W and, due to its forward positioning with respect to the fire control, the action bar 20 has not engaged the sear lock 14, and the cartridge cannot be fired. Fig. 3 shows the tool pressed against a work face in a position perpendicular thereto. The end of the action tube assembly, in addition to the entire periphery 251 (Fig. 2) of the shield, has engaged the work and, due to this engagement, the action tube assembly is rearwardly displaced within the shield assembly and the housing 16 to the extent necessary to bring the action bar 20 into engagement with and displace the sear lock 14, to clear the scar 9 and permit firing movement of the sear. Any desired variation in the range of angles departing from the perpendicular and within which firing is still possible may be provided merely by varying the over-all length of the action tube assembly.

In our consideration thus far, with the exception of the arrangement for effecting an eccentric adjustment, the present invention functions exactly as did that of the prior Catlin invention previously referred to herein. Upon firing of the cartridge, however, the improved features of our present invention come into play. In accordance with well-known physical principles, the projection of any missile, such as the studs projected by the Walker tool, is accompanied by an equal and opposite recoil reaction which may be resolved into a reaction component due to projection of the mass of the stud and a reaction component due to gas blast during the expulsion at extremely high velocity of a charge of gas having a weight equal to that of the powder charge. With the Walker tool, the total recoil reaction, which is the sum of the two components, is primarily exerted upon the barrel, which is thus forcibly retracted within the action tube and action tube extension away from the surface of the work, providing a chamber which, at maximum retraction, has a volume of less than one cubic inch. With the Walker tool, when the barrel has recoiled to an extent such that the inner surface of the housing 16 is again engaged by the forward end of the action tube 19, the action tube extension is pulled away from the surface of the work by the recoil of the barrel and the propellant gas confined therein escapes laterally at the face of the work. This much of the action on firing is common to the Walker tool and to the prior Catlin improvement. With out present invention, however, the shield box 25 surrounds and confines these escaping gases and any particles carried thereby. It is recognized that these gases are confined and tend to lift the shield, however, the shield 25 provides a substantial volume for expansion, more than four cubic inches and preferably more than sixteen cubic inches, and cooling of the expanding gases is rapid. Hence, there will seldom, if ever, be suicient force exerted by the expansion of these confined gases to materially lift the shield 25 from the face of the work against the urging of the spring 234 or to permit the escape of any significant amount of spall. The other force which might seem to tend to lift the shield from the face of the work is the reaction exerted on the barrel and all parts rigidly connected thereto. This reaction is, of course, equal in amount and opposite in sign to the kinetic energy imparted to the projected studs and the gases escaping. This recoil reaction, however, does not lift the shield 25 from the face of the work for the reason that the barrel 1 and action tube cover 16 are free to recoil together relative to the action tube 19 and tube extension 21 until the muzzle end of the action tube is engaged by the front end of the action tube cover. Thereafter, the barrel, action tube cover, action tube, and action tube extension will recoil together. However, there is a space between the pin 233 on the action tube extension 21 and the inturned shoulder 231 on the sleeve assembly of the shield 25 and, until the four members referred to in the preceding distance have recoiled together for an additional distance equal to this space, their recoil can have no effect on the shield 25, for a spring 234 is at all times compressed between the action tube cover at 161 and the shield 25. This compressed spring acts at all times to maintain the shield 25 in contact with the surface of the work and the recoil of the barrel is seldom, if ever, great enough to bring the pin 233 into engagement with the inturned shoulder 231 while an operator retains his usual grip on the handle 6 and on the housing 5. Thus, substantially no flying particles escape from the shield. As considerable of the energy of the gas is absorbed as heat during expansion of the trapped gas and the cxcess is diffused through the region between the work face and the end face 251 of the shield, the sound of the cartridge explosion is signieantly diminished.

Although we have described the preferred embodiment of our new shield with reference to the safety features employed in the Walker tool and in the prior Catlin application, it should be apparent from consideration of Fig. that many of the advantages of our present invention will be obtained by the application of a simple spring extended shield box 525 to or surrounding the muzzle of a tool employing a fixed or removable barrel 501 of a type common to several commercially available tools. For this application we have provided mounted on the shield box top 524 a sleeve 523 slidable on the barrel housing 502 and limited in its extension relative thereto by a pin 503 secured to the barrel housing and engaging an annular groove 504 in the sleeve. A spring 505, engaged between the box top 524 and a shoulder 506 on the barrel housing 502, urges the forward edge of the box to normally project a considerable distance in advance of the muzzle of the barrel. Upon engaging the shield with the work, the tool would ordinarily be rmly pressed against the surface of the work to such a degree as to bring the muzzle of the barrel into contact with the work as the shield is forced rearward along the barrel housing against the force of the spring 50S. Upon firing, the recoil reaction will withdraw the muzzle of the barrel from contact with the work, permitting the expansion of gas and the trapping of flying particles within the shield box.

Although we have specifically shown only two modications of our device, we do not intend that our invention should be considered as limited thereto. For an exact definition upon the limits of our invention, reference may be had to the appended claims.

We claim:

l. In a stud driving tool having a barrel through which a fastening device may be projected into a work surface by the combustion of an explosive propellant and having a housing for the breech end of said barrel; safety shield means comprising in combination a sleeve supported coaxially with the barrel for reciprocation on the muzzle end of the barrel, a shield box of penetration resistant material and of at least four cubic inches volume, dened by an open bottom, by a substantially continuous side wall, and by a top plate, said box being mounted on said sleeve with said barrel extending through the top plate into said shield box whereby the edge of the side wall defining the open bottom of the shield box is in engagement with the work surface surrounding the point on the work surface into which the fastener is projected and the shield box substantially completely confines any material displaced by fastener projection, and compression spring means interposed between said housing and the top plate of said shield box yieldingly urging the box away from said housing to position the edge of the side wall dening the open bottom of the box in advance of the plane of the muzzle of the barrel and thereby tend to maintain the edge of the box in engagement with the work surface and maintain confinement of material displaced from the work surface during normal recoil of the barrel away from said work surface incident to projection of the fastening device.

2. In a stud driving tool comprising a housing and a barrel and a tubular member surrounding said barrel projecting from said housing, said tool being adapted for the combustion actuated propulsion of a fastening device through said barrel and into a work surface, the combination comprising a boxlike shield of penetration resistant material having one open side, interengaging means on said tubular member and on said shield by which said shield is supported on said tubular member for reciprocation parallel to the axis of said barrel and with the open side facing in the same direction as the muzzle of said barrel, said boxlike shield being of such dimensions that the shield, together with the work surface against which said tool and shield are held, form a substantially closed chamber of at least four cubic inches volume substantially enclosing the muzzle of the barrel and adapted to receive combustion gases discharged therefrom and other material displaced by the projection of the fastening device into the work surface, and compression spring means interposed between said housing and said shield yieldingly urging the open side of said shield to project forward to a position beyond the muzzle of said barrel and thereby tend to maintain contact between said shield and the work surface during normal recoil of the tool incident to firing.

3. In a stud driving tool comprising a housing and a barrel and a safety operating action tube extension surrounding said barrel and reciprocable thereon, both projecting from said housing, said tool being adapted for the combustion actuated propulsion of a fastening device through said barrel and into a work surface, the combination comprising a boxlike shield of penetration resistant material having one open side, interengaging means on said action tube extension and on said shield by which said shield is supported on said action tube extension for reciprocation thereon along a line parallel to the axis of the barrel and with the open side facing in the same direction as the muzzle of said barrel, said boxlike shield being of such dimensions that the shield, together with the work surface against which said tool and said action tube extension are held, forms a substantially closed chamber of at least four cubic inches volume enclosing the end of the action tube extension and the muzzle of said barrel and adapted to receive combustion gases discharged from said barrel and other material displaced incident to the projection of the fastening device into the work surface, and compression spring means interposed between said housing and said shield urging the open side of said shield to project forward to a position beyond the end of said action tube extension and the muzzle of said barrel and thereby tend to maintain contact between said shield and the work surface during normal recoil of the tool incident to tiring.

vReferences Cited in the le of this patent UNrrED STATES PATENTS 2,594,275 Baisch Apr. 29, 1952 

